Fatal Error prevents me to end campaign

Once I kill the last Chosen - Zagthean in my case - I get to the speech granting me a new mission in the Caliban sector, then after the second narrative, when a new mission is about to pop, related to the main storyline I can only guess, my client is experiencing a fatal error each single time.

I tried passing a couple turns before I do this fight, tried several fleet composition, yet I can't seem to get rid of this fatal error.

Did this happen to anyone else?

Hey @Antheus
Thanks for reporting this. Could you please tell us the name of the mission you had right before the crash?